الفهرس 
Overview of Cooperative CommunicationsOnly 14 pages are availabe for public view
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Abstract
It is well known that the Multiple-Input Multiple-Output (MIMO) systems can
significantly improve the capacity and reliability of communication over fading channels
using spatial multiplexing and/or space-time coding. However, it is difficult to equip the small
mobile unit with more than one antenna with uncorrelated fading. In such case, the transmit
diversity can only be achieved through what is known as cooperative diversity, where the
users in the network share their resources and transmit cooperatively.
First, we propose a cooperative diversity protocol implementing space-time coding for an
arbitrary number of relay nodes with Amplify-and-Forward (AF) protocol, when the sourcedestination
link contributes in the second phase. We consider the use of real-orthogonal and
quasi-orthogonal designs of space-time codes as they give better performance than random
linear-dispersion codes. It is proved that the proposed protocol achieves a diversity of
order 1 N + , where N is the number of relay nodes. The optimum power allocation that
minimizes the PEP is derived using numerical and theoretical analysis.
Then, the design of a distributed Space-Frequency Code (SFC) for multipath fading relay
channels that can exploit both cooperative and multipath diversities is considered. It is shown
that the proposed code achieves a diversity of orderNL , where L is the channel memory
length. The Decode-and-Forward (DF) protocol and erroneous decoding at the relay nodes are
considered.
We also consider the design of cooperative diversity schemes for the Single-Carrier
Frequency Division Multiple Access (SC-FDMA) system in the uplink direction. Specifically,
two relay-assisted distributed space-time/frequency codes are proposed. The proposed
distributed SFC takes into account the Peak-to-Average Power Ratio (PAPR) which is a
major feature of the system. Moreover, we propose a bandwidth-efficient distributed Space-
Time Code (STC) for slow fading relay channels. DF protocol is used at the relay nodes.
Finally, we investigate the impact of cooperative communication on improving the
physical layer security. The proposed techniques select a trusted DF relay to assist the source
transmission and maximize the achievable secure rate for different eavesDROPper policies
(cooperation or not) and available channel knowledge. In addition, a jamming method that
selects two relay nodes to create an intentional interference at both phases of the DF protocol
in order to confound the eavesDROPper nodes is also considered. Simulation and analytical
results demonstrate the performance improvement of the proposed schemes.